To simplify a preceding graph as a non-determinative event record format to be used for a 'Manetho' fault tolerant system.

In the fault tolerant computer system provided with plural processors and plural recovery units A to C for operating plural processes, each of the units A to C is provided with a Jogging means for recording one action process to be operated in each processor, a message sent from an action process in its own recovery unit, and the sequence of non-determinative event information of all action processes, a history state means for maintaining the up-to-date state information of an action process in its own recovery unit, and a recovery means for starting a substitutive process by using the state information of the history state means in its own recovery unit. Consequently a preceding vector for recording the non-determinative event sequence of respective action processes is substituted for a preceding graph in a Manetho system using conventional technology.